Determining a 'safe' high-mass limit in matrix-assisted laser desorption/ionisation time-of-flight mass spectra of coal derived materials with reference to instrument noise

Three methods for determining a 'safe' estimate for high-mass limits of MALDI spectra of coal derived liquids were explored, using a sample of coal-tar pitch and its pyridine-insoluble fraction. Co-addition of increasing numbers of single-shot spectra (10, 30, 50 and 100 pulses) showed visually observable reductions in noise levels, consistent with robust and statistically meaningful signals. Three separate types of post-acquisition calculation were used to identify high-mass limits of the spectra. (i) A literature method indicated high-mass limits similar to those observed visually-as a shift from baseline at the highest masses, nearly 350 000 u for the coal tar pitch and about 390 000 u for its pyridine insoluble fraction. (ii) Comparing instrument signal with pre-selected multiples of the standard deviation, upper mass estimates of between 40-60 000 u for the coal-tar pitch and about 95 000 u for its pyridine-insoluble fraction were found. (iii) Calculation of the slope was used to identify 'lift-off' of the spectrum from baseline. The angle between the smoothed spectrum and the baseline was matched to a pre-selected value (e.g. 0.5 degrees and 1 degrees ). However, the arbitrary specification of the key parameter did not establish this last method on a firm basis. The choice of a criterion for estimating high-mass limits of MALDI spectra remains a semi-quantitative procedure; a reasonably conservative high-mass limit may be estimated by comparison of signal with five times the standard deviation. However, evaluation of size exclusion chromatograms of the present samples using polystyrene standards suggests that molecular mass distributions of pitch samples arrived at by MALDI mass spectrometry are, at least partly, determined by the limitations of available instruments. Copyright 1999 John Wiley & Sons, Ltd.     

Two-carrier conduction in Rb-TCNQ-II

Single crystal electrical resistivity and thermoelectric power (TEP) measurements as a function of temperature are repotted in Rb-TCNQ-II. Results suggest intrinsic conductivity by holes above 360 K with an activation energy of 0.44 eV. Below room temperature conductivity is extrinsic and is due to donors located 0.18 eV below the conduction band.     

Magnetic glass in shape memory alloy: Ni(45)Co(5)Mn(38)Sn(12)

The first order martensitic transition in the ferromagnetic shape memory alloy Ni(45)Co(5)Mn(38)Sn(12) is also a magnetic transition and has a large field induced effect. While cooling in the presence of a field this first order magnetic martensite transition is kinetically arrested. Depending on the cooling field, a fraction of the arrested ferromagnetic austenite phase persists down to the lowest temperature as a magnetic glassy state, similar to the one observed in various intermetallic alloys and in half doped manganites. A detailed investigation of this first order ferromagnetic austenite (FM-A) to low magnetization martensite (LM-M) state transition as a function of temperature and field has been carried out by magnetization measurements. Extensive cooling and heating in unequal field (CHUF) measurements and a novel field cooled protocol for isothermal MH measurements (FC-MH) are utilized to investigate the glass like arrested states and show a reverse martensite transition. Finally, we determine a field-temperature (HT) phase diagram of Ni(45)Co(5)Mn(38)Sn(12) from various magnetization measurements which brings out the regions where thermodynamic and metastable states coexist in the HT space, clearly depicting this system as a 'magnetic glass'.     

Syntheses and reactions of some fluorinated dienes,cyclobutenes and furans

There are many reports¹ of the pyrolysis of fluorinated organic compounds, including the defluorination of cyclic fluorocarbons over iron to give aromatic compounds. Extending this technique we have investigated the flow pyrolysis of some readily accessible unsaturated fluorocarbons, such as I, II, and III, and found these to be synthetically

useful routes to fluorinated dienes, cyclobutenes, and furans. Pyrolyses were carried out using a nitrogen flow over platinum, iron or caesium fluoride heated at 430–700°. The various products can all be rationalized in terms of intermediate allylic radicals, and the solid substrate influences which allylic radicals are formed.We are also investigating the chemistry of those now accessible compounds, such as IV, V, and VI, and some of the preliminary results are described.

For example the fluoride ion induced dimerisation of IV gave two major products VII and VIII via a particular interesting mechanism.

     

Ultrasonic studies of aluminium-substituted Bi(Pb)-2223 superconductors

The compositional dependence of elastic properties of Al³⁺-substituted Bi(Pb)-2223 superconducting system with the general formula Bi_1.7−x Al_xPb_0.3Sr₂Ca₂Cu₃ O_y (x = 0.0, 0.1, 0.2 and 0.3) have been studied by means of ultrasonic pulse transmission (UPT) technique at 1 MHz (300 K). The elastic moduli of the specimens are computed and corrected to zero porosity. The observed variation of elastic constants with aluminium substitution has been explained on the basis of the strength of interatomic bonding. The applicability of heterogeneous metal mixture rule for estimating elastic constants and transition temperature has been tested.     

Improvement in hygroscopic property of macro-defect free cement modified with hypromellose/potassium methyl siliconate copolymer and pulverized fly ash

Journal of Thermal Analysis and Calorimetry - Macro-defect-free (MDF) cement composites are high-strength materials produced by applying high shear to cement-polymer pastes, using twin roller mill...     

Effect of reverse substrate bias on the minigap in Si inversion layers

The influence of a reverse substrate bias on the minigap of Si inversion layers on (10, 1, 1) and (8, 1, 1) surfaces has been investigated. Substrate bias shifts the position of the gap to higher gate voltages but the center of the gap remains at a fixed mobile charge density. Reverse bias increases the magnitude of the minigap by as much as 30%.     

Orientation dependence of the memory echo in piezoelectric powders

Observation of two pulse and memory echoes in TeO₂ powder is reported. An electric field rotation experiment on the reading pulse gives a cos²θ dependence of the echo amplitude. This is in apparent disagreement with the predictions of the orientation model.     

Fine structure in the field effect mobility of MOS transistors

We have studied the fine structure in the field effect mobility of MOS transistors at 4.2 K. With applied substrate bias, the position in gate voltage of the structure is unchanged and the amplitude decreases. The position of the structure is also unchanged by normal magnetic fields of up to 150 kgauss. We have studied samples with four equivalent source-drain contacts. The structure depends strongly on the contacts. The structure in the field effect mobility appears to be due to the contacts and not a property of the inversion layer or surface states.